This application claims the benefit of Korean Application No. 2002-3854, filed Jan. 23, 2002 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a color cathode ray tube (CRT), and more particularly, to a tension mask frame assembly for a color CRT which reduces vibrations of the tension mask supported by the frame.
2. Description of the Related Art
In a typical color CRT, such as that shown in FIG. 1, three electron beams are emitted from an electron gun 3 installed at a neck portion 2 of a funnel 1. The electron beams pass through electron beam passing holes 4a of a shadow mask 4 having a color selection function and land on red, greed and blue fluorescent substances of a fluorescent film 6 formed at an inner surface of a panel 5 sealed with the funnel 1. Thus, as the fluorescent substances are excited, an image is formed.
A screen surface of the above color CRT is made flat to widen a view angle and prevent distortion of an image. Accordingly, a mask installed inside a color CRT and having a color selection function must be made flat. Making flat masks is one of the obstacles in the manufacture of flat screen color CRTs.
FIG. 2 shows an example of a tension mask frame assembly for a flat CRT. As shown in the drawing, a tension mask frame assembly for a flat CRT includes a frame having first and second support members 11 and 12 installed parallel to each other. Each of first and second rigid members 13 and 14 have both end portions fixed to corresponding ends of each of the first and second support members 11 and 12. A tension mask 20 has opposite edges thereof (i.e., long sides) that are welded to the support members 11 and 12 so that tension is applied. The tension mask 20 has a plurality of strips 21 which are separated a predetermined distance from one another and each includes slits 22. Adjacent slits 22 within each strip 21 of the tension mask 20 are divided by a real bridge 23 which connect the adjacent slits 22 at a predetermined interval.
In the tension mask frame assembly having the above structure, since the edges of the long sides of the tension mask 20 are fixed to the first and second support members 11 and 12, the short sides of the tension mask 20 are free in a direction Y which is perpendicular to a direction X (i.e., in a perpendicular direction with respect to one side surface of the tension mask 20). Thus, the tension mask 20 supported by the frame 10 can be vibrated by an impact applied from the outside or sound pressure generated by a speaker. The vibration prevents the electron beams emitted from the electron gun 13 from accurately passing through the sits 22. Thus, the amount of the electron beams passing through the slits 22 changes.
Additionally, the mislanding of the electron beams causes a loss of a color or an allochromatic color of the electron beam landing on the fluorescent film, so that a uniform resolution of an image cannot be obtained. In particular, since the inside of a CRT is a vacuum, there is no air resistance and the vibration of the mask continues for a long time. Thus, there needs to be a damper which quickly damps vibrations by converting vibration energy into another energy.
A conventional tension mask frame assembly for reducing vibrations by using the damper operation is disclosed in Japanese Patent Publication No. hei 12-77007. In the disclosed tension mask frame assembly, the amplitude of the short side portion of the tension mask is relatively uniform compared to that of the center portion thereof under the 7th tension mask resonance mode. The tension mask frame assembly has a structure in which vibrations are reduced by inserting clips or rings into a non-hole portion at the short side portion of the tension mask.
In the meantime, a tension mask frame assembly to reduce a vibration reduction effect at the center portion of the tension mask and in the direction X has been developed by the Display Device Research LAB of LG-Philips Displays. In the tension mask frame assembly, both end portions of a ball chain are fixedly installed in an ineffective area of a tension mask supported by a rail (fixed to a panel). Here, it is difficult to attach the ball chain to the ineffective area and a satisfactory vibration reduction effect at the center portion cannot be expected.
To solve the above and other problems, it is an aspect of the present invention to provide a tension mask frame assembly for a color CRT which improves a vibration reduction effect by reducing vibration energy due to a non-elastic collision of the tension mask supported at the frame and further prevents oscillation of an image and improves resolution by preventing a mislanding of an electron beam on the fluorescent film.
It is another aspect of the present invention to provide a tension mask frame assembly for a color CRT which improves a vibration reduction effect in a lengthwise direction of the tension mask supported at the frame.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and for other aspects, there is provided a tension mask frame assembly for a color CRT which includes a tension mask having an effective area including a plurality of electron beam passing holes through which electron beams pass and an ineffective area disposed at an edge portion of the effective area, a frame including support members which support opposite side portions of the tension mask so that tension is applied to the tension mask and rigid members which support end portions of the support members to maintain a gap between the support members, and at least one weight member installed by a fixing unit to be separated at a predetermined interval in the ineffective area of the tension mask in a lengthwise direction of the tension mask fixed at the frame.
According to an aspect of the present invention, the fixing unit is attached in the ineffective area to be separated a predetermined distance from the surface of the ineffective area and which is capable of vibrating relative to the surface.
According to another aspect of the present invention, a weight per unit area of the weight member is over 10 times a weight per unit area of the tension mask.